The kinetics of passage of 125I-labeled immunoglobulins and antibodies of different classes and subclasses from blood to cerebrospinal fluid will be followed in normal hamsters whose blood-brain barrier has been damaged by chemicals or by measles infection of the central nervous system (CNS). Hypermolaric concentrations of urea which cause opening of tight junctions of the blood-brain barrier and 4 (2 N-piperidinoethyl) piperidine which causes hydropic degeneration of the choroid plexus will be the chemicals used in the study. Damage to the blood-brain barrier by these chemicals is reversible with time. Kinetics of passage of subpopulations of lymphoid cells from immunized donors into the CNS of recipient hamsters will also be determined. Recipient hamsters will be normal animals or animals infected with measles virus or chemically treated as described. Information obtained from these studies on the route of passage and kinetics of ingress from blood to CNS of antibodies and antibody-forming cells and their length of stay in the CNS as functioning elements should aid in an understanding of their presence in the CNS of patients with multiple sclerosis and other CNS diseases of obscure origin.